The present invention relates generally and in various embodiments to communications systems. More specifically, the present invention relates generally and in various embodiments to satellite digital audio service (SDARS) apparatuses, systems, and methods.
Although various implementations of the present invention, among many, may be described herein with reference to the specific illustrative embodiments related to particular applications, those skilled in the art will understand that the invention is not in any way intended to be limited to such embodiments and/or applications. Those having ordinary skill in the art and reference to the description of the embodiments herein will recognize additional modifications, applications, and other embodiments falling within the scope of the claimed invention and additional fields in which the present invention may be practiced.
Digital Radio (also known as Satellite Radio or Satellite Digital Audio Radio Service (SDARS)) is a subscriber-based digital radio service that is broadcast via satellites. Digital radio service provides compact-disc (CD) quality programming that may be digitally transmitted via one or more satellites and/or space stations to one or more Earth-based (terrestrial) digital radio stations, receivers, and/or repeaters. In satellite-based direct-broadcast radio services, digitally-encoded audio program material may be broadcast to terrestrial fixed or mobile digital radio receivers. Fixed receivers may include, for example, stand alone digital radio receivers or digital radio receivers connected via computer networks, including for example, the Internet. Mobile receivers may include, for example, digital radio receivers located in automobiles, aircrafts, watercrafts, and the like.
Satellite-based digital audio radio services such as SDARS, for example, may be broadcast to one or more digital radio receivers either directly from an orbiting satellite, or indirectly from one or more repeater stations. Such repeater stations may be useful where the digital radio receiver is located in a shielded location or where there is no direct line of sight between the radio and the satellite. In other digital audio radio services systems, the audio programs also may be transmitted in digital form by one or more space stations directly to fixed, mobile, and/or portable radio stations. Such systems may comprise, for example, orbiting satellites, complementary repeating terrestrial transmitters, telemetry, tracking, and control facilities.
The digital radio format of SDRAS systems may utilize, for example, various properties of software defined radio and may comprise a receiver and/or a transmitter device, where each device is capable of digitizing a received signal and then processing the digitized signal using digital signal processing techniques. The signals may be digitized (i.e., undergo analog-to-digital conversion) at the Radio Frequency (RF), Intermediate Frequency (IF), or baseband frequency stages. The modulated analog signal to be transmitted by the radio station, repeater, satellite, and/or space station initially may be generated as a digital signal using digital signal processing techniques and then converted to an analog signal for transmission. The signals may undergo digital-to-analog conversion at the baseband, IF, or RF stages. Fundamental characteristics of the digital radio may be changed using basic software programmability. Therefore, the modulation scheme, operating frequencies, bandwidths, multiple access schemes, source, and channel coding/decoding methods, frequency spreading/despreading techniques, and encryption/decryption techniques may be readily changed.